The invention concerns an X-ray optical configuration, comprising                a position for an X-ray source,        a position for a sample,        a first focusing element for directing X-ray radiation from the position of the X-ray source via an intermediate focus onto the position of the sample, and        an X-ray detector which can be moved along a circular arc of radius R around the position of the sample.        
An X-ray optical configuration of this type is disclosed in U.S. Pat. No. 6,807,251 B2 and in the leaflet Bruker AXS GmbH; Karlsruhe, Germany, “Diffraction Solutions D8 Advance” 2002.
X-ray diffractometry may be used for diverse analytical tasks, in which different measuring geometries are used, e.g. Bragg-Brentano or parallel beam geometry. This requires, however, different X-ray optical elements in the optical path. In order to enable fast change between the various measuring geometries, it is desired to keep the necessary modification measures at a minimum level.
U.S. Pat. No. 6,807,251 B2 discloses an X-ray diffractometer with a parabolic mirror for use of the diffractometer in parallel beam geometry, and a slotted plate with two slots, wherein one of the slots is used to delimit the X-ray beam in the Bragg Brentano geometry. The mirror and the slotted plate are rigidly connected to each other. A rotatable path selection disk with a further slot is disposed behind the aperture/mirror unit and can be rotated to select the X-ray beam (parallel or divergent) that is required for the corresponding geometry.
DE 101 41 958 A1 discloses an X-ray diffractometer, in which the X-ray radiation can be guided in sections on different beam paths for a variety of tasks, wherein one of the beam paths extends in a straight line from the sample through an aperture system with adjustable and/or exchangeable apertures to the X-ray detector, whereas the other beam path is bent, extending initially from the sample position to a dispersive or reflecting X-ray optical element, and from there to the X-ray detector. The bent beam path can be collimated out with respect to the detector by means of the shutter. The aperture and the dispersive or reflecting X-ray optical element are adjusted in a rigid fashion with respect to each other and can be pivoted together with respect to the sample.
Diffractometers are often not only used to measure samples in reflection geometry (such as e.g. powder samples) but also samples in transmission geometry (such as e.g. foils or capillaries). Towards this end, the X-ray optical configuration of conventional X-ray diffractometers must be manually modified as is schematically indicated e.g. in the mentioned leaflet of Bruker AXS GmbH on page 13 and 14, respectively.
The modification of X-ray optical elements turns out to be disadvantageous in practice, since the modified X-ray optical elements must be readjusted each time. This is an extremely time-consuming process which must also be performed by qualified staff.
Moreover, some of the X-ray optical components, such as e.g. focusing crystals or holders, must be exchanged in most cases, which requires careful storage of the currently not required X-ray optical components. The expensive X-ray optical components are therefore subjected to an increased risk of being damaged or even getting lost during modification and storage.
In contrast thereto, it is the underlying purpose of the present invention to propose an X-ray optical configuration which facilitates change between reflection geometry and transmission geometry, in particular, in which modification and adjustment works are minimized or superfluous.